The present invention relates to a field repairable, heavy duty circular saw blade having an exceptionally long operating lifetime. The blade is particularly useful for felling small to medium sized trees when used in conjunction with available feller/buncher equipment.
In the past ten years automated felling and log bunching equipment has had a major increase in usage where the forestland is of moderate topography. This popularity is in large part due to the productivity gain and cost reduction when compared with individual loggers using chain saws. Some of this equipment is capable of harvesting tree stems at rates of 200 per hour when used under the most favorable conditions. Most mechanical felling equipment operates at much lower rates, however.
One of the popular types of mechanical harvesters in wide use today employs very heavy duty hydraulically operated shears to sever the tree from its stump. The use of these shears has resulted in a significant productivity gain, but this has not been without certain cost. Very often severe stress are induced in the lower part of the tree trunk which later result in splits and/or checking when the tree is processed into lumber.
More recently, harvesters have become available using large heavy duty circular saws to sever the trees. These have been quite successful in reducing stress damage in the butt portion of the log. However, the saw blades are quite expensive and their maximum life under field conditions has been far below expectations. In many cases blade life has been below 100 hours before destruction occurred due to accidental contact with a rock or similar object. In addition to the expense of replacing a dull or destroyed blade, installation of a new blade in the field is not a simple matter because the blades are very heavy.
Most of the circular saw blades available for the purpose described above are simply heavier duty versions of conventional circular saw blades used in sawmills. These may either have the teeth formed integrally around the circumference of the saw plate or the teeth can be individually inserted in locations provided around the periphery. In either case, the expensive saw plate itself is readily subject to damage and often is beyond repair when such damage has occurred.
Numerous designs of composite types of circular saws have been developed over the years. Many of these have as one object the preservation of the relatively expensive saw plate. A favorite design has been the use of individual segments riveted or bolted around the periphery of the saw plate. In almost all instances these have been attached by an arrangement in which the periphery of the plate is turned or ground into a tongue which mates with an equivalent groove in the individual segments. In most cases each segment will have several teeth permanently formed around its periphery. In one or more teeth are severely damaged, the entire segment is then replaced. Saws of this type are seen in U.S. patents to Fullerton, No. 2,544,920; Hiltebrand, No. 2,670,766; Jagers, and No. 4,102,231; French Pat. No. 1,120,121; and German Pat. No. 579,558. U.S. Pat. No. 4,257,302 to Heimbrand, et al. shows a similar arrangement in which the individual segments have inserted rather than permanent teeth. In somewhat related patents, Reising, U.S. Pat. No. 3,419,976, shows a ditching wheel in which the teeth themselves have a saddle shaped base to straddle a plate. Each individual tooth is simply bolted to the plate. Adcock, U.S. Pat. No. 3,804,138, shows a brush cutting outrigger for use on the front of a crawler type tractor. Each individual tooth has a socket in its base and is pinned to a corresponding tongue on one of the brush cutter blade members. To date, none of these designs have been found generally satisfactory either for sawmill use or for field use in forest tree cutting. The blades have either been too complex or could not be built in a form which was sufficiently rugged.